Continuous time sigma-delta A/D converter and electrical system comprising the A/D converter

Abstract

A continuous time sigma-delta analog-to-digital converter comprising: a summator of an input analog signal and a feedback signal; a feed-forward integrator path connected to the summator and configured to provide a digital signal; a feedback digital-to-analog converter to convert the digital signal into a feedback analog signal; a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summator.

1. A continuous time sigma-delta analog-to-digital converter comprising:
 a summer configured to provide a difference signal equal to a difference between an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the summer and configured to provide a digital signal, the feed-forward integrator path including:
 an operational amplifier in an integrator configuration having:
 a first operational amplifier input electrically connected to the summer; 
 a second operational amplifier input; and 
 an operational amplifier output; 
 
 a feedback capacitor having a terminal connected to the operational amplifier output; and 
 an electrical link connecting another terminal of said feedback capacitor to the operational amplifier input; 
 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summer. 
 
     
     
       2. The analog-to-digital converter of  claim 1 , wherein the feed-forward integrator path further includes:
 a low pass filter connected to the operational amplifier output; and 
 a quantizer interposed between the low pass filter and a digital output for said digital signal. 
 
     
     
       3. The analog-to-digital converter of  claim 1 , wherein the electrical link includes a feedback resistor connected in series to the feedback capacitor so as to introduce a zero in a signal transfer function associated with the analog-to-digital converter. 
     
     
       4. The analog-to-digital converter of  claim 1 , wherein said feedback low pass filter is an RC filter and is configured to introduce a pole into a signal transfer function associated with the analog-to-digital converter. 
     
     
       5. The analog-to-digital converter of  claim 4 , wherein the feedback low pass filter comprises:
 a filter capacitor placed between an output of the feedback digital-to-analog converter and a voltage reference; and 
 a filter resistor connected between the output of the feedback digital-to-analog converter and the summer. 
 
     
     
       6. The analog-to-digital converter of  claim 5 , wherein the feed-forward integrator path comprises:
 a feedback resistor connected in series with the feedback capacitor between the operational amplifier output and input so as to introduce a zero in a signal transfer function associated with the analog-to-digital converter, wherein electrical parameters associated with the filter capacitor, the filter resistor, the feedback resistor and the feedback capacitor are designed to obtain a frequency associated with the pole equal to a frequency associated with the zero. 
 
     
     
       7. The analog-to-digital converter of  claim 1 , further comprising an input low pass filter configured to filter the input analog signal, associated with said summer, and connected to said feed-forward integrator. 
     
     
       8. The analog-to-digital converter of  claim 7 , wherein the input low pass filter comprises:
 a first input resistor connected between a first terminal configured to receive the input analog signal and a second terminal; 
 a second input resistor connected between the second terminal and the first input of the operational amplifier; 
 a input capacitor connected between the second terminal and the second input of the operational amplifier. 
 
     
     
       9. The analog-to-digital converter of  claim 8 , wherein:
 said feedback low pass filter is an RC filter, is configured to introduce a first pole into a signal transfer function associated with the analog-to-digital converter, and includes:
 a filter capacitor placed between an output of the feedback digital-to-analog converter and a voltage reference, and 
 a filter resistor connected between the output of the feedback digital-to-analog converter and the summer; 
 
 the input low pass filter is configured to introduce a second pole into the signal transfer function associated with the analog-to-digital converter; and 
 the respective electrical parameters associated with the filter capacitor, the filter resistor, the first and second input resistors, and the input capacitor are selected to obtain the first pole equal to the second pole. 
 
     
     
       10. The analog-to-digital converter of  claim 1 , wherein the feedback digital-to-analog converter comprises:
 a digital input coupled to receive said digital signal; 
 a current terminal configured to supply an analog current pulse corresponding to the feedback analog signal; 
 a current mode converter electrically connected to the digital input and the current terminal; 
 a timing input structured to receive a clock signal configured to drive said current mode converter; and 
 a shaping filter electrically connected between the timing input and the current mode converter and configured to shape said analog current pulse. 
 
     
     
       11. The analog-to-digital converter of  claim 10 , wherein the current mode converter comprises:
 a differential pair circuit structured in a common emitter configuration; 
 a diode connected to a common emitter terminal of the differential pair circuit; 
 wherein the differential pair circuit is configured to be switched off/on by the clock signal. 
 
     
     
       12. The analog-to-digital converter of  claim 11 , wherein the shaping filter comprises:
 a shaping resistor electrically connected to the timing input; 
 a shaping capacitor electrically connected to said shaping resistor and said diode; 
 wherein the feedback digital-to-analog converter is structured to cause the clock signal to charge said shaping capacitor in a first configuration and discharge said shaping capacitor in a second configuration and via said differential pair circuit to produce said analog current pulse. 
 
     
     
       13. The analog-to-digital converter of  claim 11 , wherein the differential pair circuit comprises:
 a first transistor having:
 a first control terminal connected to the digital input to receive said digital signal; and 
 a first output terminal connected to the current terminal to supply the analog current pulse; 
 
 a second transistor having:
 a second control terminal configured to receive the opposite of said digital signal; and 
 a second output terminal to provide a further analog current pulse. 
 
 
     
     
       14. The analog-to-digital converter of  claim 10 , wherein the feedback digital-to-analog converter is a one-bit return-to-zero converter. 
     
     
       15. The analog-to-digital converter of  claim 10 , wherein the feedback digital-to-analog converter further includes an additional current mode converter electrically connected to the digital input and the current terminal. 
     
     
       16. The analog-to-digital converter of  claim 1 , wherein the analog-to-digital converter is realized according to a BiCMOS technology. 
     
     
       17. An electrical system comprising:
 a continuous time sigma-delta analog-to-digital converter including:
 an input terminal structured to receive an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the input terminal and configured to provide a digital signal, the feed forward integrator path having:
 an operational amplifier in an integrator configuration, an input of the operational amplifier electrically connected to the input terminal; and 
 a feedback capacitor having a terminal connected to an output of the operational amplifier; 
 
 an electrical link connecting another terminal of said feedback capacitor to the input of the operational amplifier; 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the input terminal; and 
 
 a processing apparatus connected to said analog-to-digital converter and configured to process the digital signal. 
 
     
     
       18. The electrical system of  claim 17 , wherein said a feedback low pass filter is an RC filter and is configured to introduce a pole into a signal transfer function associated with the analog-to-digital converter. 
     
     
       19. The electrical system of  claim 17 , wherein:
 said electrical system is a car radio turner system, and 
 said apparatus comprises a demodulator of said digital signal. 
 
     
     
       20. A continuous time sigma-delta analog-to-digital converter comprising:
 a summer configured to provide a difference signal equal to a difference between an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the summer and configured to provide a digital signal; 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summer, wherein said feedback low pass filter is an RC filter and is configured to introduce a pole into a signal transfer function associated with the analog-to-digital converter. 
 
     
     
       21. The continuous time sigma-delta analog-to-digital converter of  claim 20 , wherein the feedback low pass filter comprises:
 a filter capacitor placed between an output of the feedback digital-to-analog converter and a voltage reference; and 
 a filter resistor connected between the output of the feedback digital-to-analog converter and the summer. 
 
     
     
       22. The continuous time sigma-delta analog-to-digital converter of  claim 21 , wherein the feed-forward integrator path comprises:
 an operational amplifier in a integrator configuration having:
 an operational amplifier input electrically connected to the summer; and 
 an operational amplifier output, 
 
 a feedback capacitor having a terminal connected to the operational amplifier output; and 
 a feedback resistor connected in series with the feedback capacitor between the operational amplifier output and input so as to introduce a zero in a signal transfer function associated with the analog-to-digital converter, wherein electrical parameters associated with the filter capacitor, the filter resistor, the feedback resistor and the feedback capacitor are designed to obtain a frequency associated with the pole equal to a frequency associated with the zero. 
 
     
     
       23. A continuous time sigma-delta analog-to-digital converter comprising:
 a summer configured to provide a difference signal equal to a difference between an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the summer and configured to provide a digital signal, the feed forward integrator path including:
 an operational amplifier having first and second inputs and an output; 
 a feedback capacitor having a terminal connected to the operational amplifier output; and 
 an electrical link connecting another terminal of said feedback capacitor to the first input; 
 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summer; and 
 an input low pass filter configured to filter the input analog signal, associated with said summer, and coupled to said feed-forward integrator, wherein the input low pass filter comprises:
 a first input resistor connected between a first terminal configured to receive the input analog signal and a second terminal; 
 a second input resistor connected between the second terminal and the first input of the operational amplifier; and 
 a input capacitor connected between the second terminal and the second input of the operational amplifier. 
 
 
     
     
       24. The continuous time sigma-delta analog-to-digital converter of  claim 23 , wherein:
 said feedback low pass filter is an RC filter, is configured to introduce a first pole into a signal transfer function associated with the analog-to-digital converter, and includes:
 a filter capacitor placed between an output of the feedback digital-to-analog converter and a voltage reference, and 
 a filter resistor connected between the output of the feedback digital-to-analog converter and the summer; 
 
 the input low pass filter is configured to introduce a second pole into the signal transfer function associated with the analog-to-digital converter; and 
 the respective electrical parameters associated with the filter capacitor, the filter resistor, the first and second input resistors, and the input capacitor are selected to obtain the first pole equal to the second pole. 
 
     
     
       25. A continuous time sigma-delta analog-to-digital converter comprising:
 a summer configured to provide a difference signal equal to a difference between an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the summer and configured to provide a digital signal, wherein the feedback digital-to-analog converter includes:
 a digital input coupled to receive said digital signal; 
 a current terminal configured to supply an analog current pulse corresponding to the feedback analog signal; 
 a current mode converter electrically coupled to the digital input and the current terminal; 
 a timing input structured to receive a clock signal configured to drive said current mode converter; and 
 a shaping filter electrically connected between the timing input and the current mode converter and configured to shape said analog current pulse; 
 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summer. 
 
     
     
       26. The continuous time sigma-delta analog-to-digital converter of  claim 25 , wherein the current mode converter comprises:
 a differential pair circuit structured in a common emitter configuration; 
 a diode connected to a common emitter terminal of the differential pair circuit; and 
 wherein the differential pair circuit is configured to be switched off/on by the clock signal. 
 
     
     
       27. The continuous time sigma-delta analog-to-digital converter of  claim 25 , wherein the feedback digital-to-analog converter is a one-bit return-to-zero converter. 
     
     
       28. An electrical system comprising:
 a continuous time sigma-delta analog-to-digital converter including:
 an input terminal structured to receive an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the input terminal and configured to provide a digital signal; 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the input terminal, wherein said a feedback low pass filter is an RC filter and is configured to introduce a pole into a signal transfer function associated with the analog-to-digital converter; 
 
 a processing apparatus coupled to said analog-to-digital converter and configured to process the digital signal. 
 
     
     
       29. The electrical system of  claim 28  wherein the feedback digital-to-analog converter is a one-bit return-to-zero converter. 
     
     
       30. A car radio tuner system comprising:
 a continuous time sigma-delta analog-to-digital converter including:
 an input terminal structured to receive an input analog signal and a feedback signal; 
 a feed-forward integrator path connected to the input terminal and configured to provide a digital signal; 
 a feedback digital-to-analog converter configured to convert the digital signal into a feedback analog signal, the feedback digital-to-analog converter including an additional current mode converter electrically connected to the digital input and the current terminal; and 
 a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the input terminal; 
 
 a processing apparatus connected to said analog-to-digital converter and configured to process the digital signal, wherein said apparatus comprises a demodulator of said digital signal.